Synthesis and characterization of transition metal complexes of Para-aminosalicylic acid with evaluation of their antioxidant activities

Article abstract of DOI:10.13005/ojc/330308

Complexing behavior of Para-aminosalicylic acid (PAS) towards Mn(II), Fe(II), Co(II), Ni(II), Cu(ii), Zn(II), have been examined by Conductance and magnetic measurements and by UV-visible, IR and ¹H NMR. Thermal decomposition properties of the

Full text of DOI:10.13005/ojc/330308

ISSN: 0970-020 X
CODEN: OJCHEG
2017, Vol. 33, No. (3):
Pg.1120-1126
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
Synthesis and Characterization of Transition Metal
Complexes of Para-Aminosalicylic Acid With Evaluation of
Their Antioxidant Activities
ABDUL BASIT WANI1*, JOGINDER SINGH2 and NIRAJ UPADHYAY3
1Department of Chemistry, Lovely Professional University, Punjab, India.
2Department of Biotechnology, Lovely Professional University, Punjab, India.
3Department of Chemistry, Dr. Hari Singh Gour University, Madhya Pradesh, India.
*Corresponding author E-mail: wanibasit.chem@gmail.com
http://dx.doi.org/10.13005/ojc/330308
(Received: April 24, 2017; Accepted: May 20, 2017)
ABSTRACT
Complexing behavior of Para-aminosalicylic acid (PAS) towards Mn(II), Fe(II), Co(II), Ni(II),
Cu(ii), Zn(II), have been examined by Conductance and magnetic measurements and by UV-
1
visible, IR and H NMR. Thermal decomposition properties of the complexes are investigated by
thermogravimetric analysis (TGA). The free ligand and its complexes were tested for antioxidant
activity and evaluation of IC50 values. It was found that PAS and its all complexes have low IC50 value
than standard ascorbic acid. All complexes have lower IC50 value than PAS with Ni complex the least
value. . Therefore, PAS and its complexes with these metal ions can act as antioxidants to reduce
oxidative stresses.
Keywords: Para-aminosalicylic acid, metal complexes, thermal analysis,
antioxidant activity, IC50
INTRODUCTION
of cancer and inflammatory bowel disease2. PAS
also has modest activity against Influenza virus
A3, 4. PAS is one of the first anti-tuberculosis agents
found to be effective in 1940s5. Today, PAS is used
primarily as a second-line drug to treat multi drug
resistanttuberculosis6.PAS, a bacteriostatic agent, is
extremely helpful in controlling the growth of bacteria.
It is also very useful in avoiding the development of
the resistance of bacteria to the other anti-multi drug
resistant -tuberculosis drugs7.
4-amino-2-hydroxy-benzoic acid or
4-aminosalicylicacidcommonlyknownaspara-amino
salicylic acid (PAS), an amine derivative of salicylic
acid, is an antibiotic and one among theWorld Health
Organization’s List of Essential Medicines. PAS is a
well-known antibacterial drug used in combination
with first line drugs like isoniazid, rifampicin, etc1.
Recently, PAS has been found effective in treatment

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WANI et al., Orient. J. Chem., Vol. 33(3), 1120-1126 (2017)
Various studies have been carried out effective reducing agent and free radical scavenger,
to examine the effectiveness of anti-inflammatory in addition to its antiscorbutic action17.The antioxidant
drugs as scavengers of reactive oxygen species activity was calculated on the basis of its radical
(ROS), viz. superoxide radical (2O•-), hydrogen scavenging activity (RSA) (percentage of inhibition)
peroxide (H2O2), hydroxyl (HO•), and hypochlorous and IC50 (total antioxidant necessary to decrease the
acid (HOCl)8. Halli well and Gutteridge (1985) have initial DPPH radical by 50%) values.
reported that non-steroidal anti-inflammatory drugs
(NSAIDs) are powerful free radical scavengers9.
Further, it is reported that NSAID, including analogs
MATERIALS AND METHODS
of salicylates, can exert neuroprotective effect Synthesis of metal complexes
by blocking inflammatory processes in neuro
All chemicals used were of analytical
degenerative diseases10.Therefore, PAS, being a reagent grade (AR), and of highest purity available.
salicylate analog, is expected to have the capacity Synthesis was carried out by the procedure as
of radical scavenging and hence can act as an used by Soliman and Mohamed (2013) with minor
antioxidant to reduce oxidative stress.
alteration. The metal complexes were prepared by
the addition of aqueous solution of the appropriate
As a derivative of salicylic acid, PAS metal acetates to the methanolic solution of SA in
acts as a metal chelator11, is clinically effective 1: 2 ratio. The resulting mixture was stirred for 3h at
drug for treatment of serious chronic manganese room temperature and simultaneously checked for
poisoning12, 13. This chelating tendency of PAS can the reaction progress.The complexes were collected
be exploited for the formation of essential metal after slow evaporation of the solvent, then washed
complexes which are useful for having better with methanol and air dried18.
biological activities especially antioxidant activities.
Further, these metal complexes are gaining attention Instruments
because of their diverse applications in almost all
Melting points were calculated on BUCHI
fields of life.More specifically the medicinal properties melting point B-545 and molar conductance of
of essential metal ion chelates are fascinating14. solid chelates in methanol were measured using
There is also a need to explore the role of trace conductometer (Labtronics-Model LT-16). Infrared
elements, essential elements or micronutrients (in spectra were recorded on Shimadzu FT-IR type FTIR-
their native or chelate forms) both in plants and 8400S spectrometer. Electronic transitions, reaction
animals and to explain their specific and extended progress and antioxidant activity were measured on
roles at various stages15.
Shimadzu UV ProbeVersion 2.33 spectrophotometer.
The molar magnetic susceptibility was measured on
Considering these literature links, the powdered samples using the Faraday method. The
complexation behavior of PAS with essential diamagnetic corrections were made by Pascal’s
metal ions viz. Manganese (Mn), Iron (Fe), Cobalt constant and Hg[Co(SCN)4] was used as a calibrant.
(Co), Nickel (Ni), Copper (Cu) and Zinc (Zn) has The 1H NMR spectra were recorded using Bruker
been studied in vitro. The PAS and the prepared Avence II 400 NMR spectrometer at SAIF PU
complexes were tested for antioxidant activities with Chandigarh. Thermo gravimetric analysis was
1,1-Diphenyl-2-picryl-hydrazyl (DPPH). Scavenging carried out at STIC Cochin, Kochi at a heating rate
of DPPH radical is the basis of the popular DPPH of 20 oC/min.
antioxidant assay. Therefore, rate of reduction of a
chemical reaction upon addition of DPPH is used as Antioxidant activity
an indicator of the radical nature of that reaction16.
The antioxidant activity in terms of free
The antioxidant activities obtained in this manner radical scavenging activity (RSA) of PAS and its
were then compared with a positive control, Vitamin complexes were measured by using 1, 1- diphenyl-
C/Ascorbic acid (AA). AA is regarded as the most 2-picrilhydrazyl (DPPH) assay.20, 40, 60, 80, 100mL
important water-soluble micronutrient in human of 100 ppm ethanolic solution of each compound
plasma and mammalian cells, required for multiple were mixed with 4 mL of 0.1mM ethanolic solution of
biological functions. In biological systems, AA is an DPPH.The mixture was shaken vigorously and left to

WANI et al., Orient. J. Chem., Vol. 33(3), 1120-1126 (2017)
1122
stand for 30 minutes in the dark.The absorbance was
then measured at 517nm against a blank.The control
was prepared, as above, without any complex added
and ethanol was used for the base line correction.AA
was used as the reference (positive control) with the
same concentrations as of PAS and its complexes.
RSA was expressed as percentage inhibition and
calculated as:
free values (Table 1).The magnetic moment values
for Mn(II), Fe(II), Co(II), Ni(II) and Cu(II) complexes
indicate the high spin octahedral nature of these
complexes.
The geometry of the metal complexes
has been assumed from magnetic moment data
and the electronic spectra of the complexes. The
electronic spectra of the ligand, recorded by UV
visible spectroscopy, show three bands at 208,
262 and 293nm (Table 1) which are attributed to
the benzene ring p → p* transitions and to the
chromophoresn → p* transitions, respectively.These
bands were shifted in the electronic spectra of the
complexes to 214–239, 261-184 and 290–315 nm,
respectively23.
RSA = (Absorption of control“ Absorption of sample)
/ Absorption of control x 10019.
IC50 values were calculated from the regression of
the plotted graph of RSC against the concentrations
of the samples20.
RESULTS AND DISCUSSION
The UV spectrum Ni(II) complex shows two
bands at 590 and 560nm which may be assigned
to 3A2g(F) →3T2g(F) and 3A2g(F) →3T1g(F) transitions,
thereby suggesting octahedral geometry of Ni(II)
complex23 22. UV spectrum of the Cu(II) complex
shows a band at 718nm, suggesting the existence
The binary transition metal complex
formation with PAS with the evaluation of radical
scavenging activity in terms of IC50have been studied
first time, and may be an area of interest because
these complexes may affect the bio availability of
PAS as these metal ions are present in relatively
appreciable concentration in biological fluids21.
2
of Eg→2T1g transition which is consistent with an
octahedral (more specifically distorted octahedral)
configuration24.
Molar conductance measurements
IR Analysis
Metal chelates are dissolved in methanol
and the molar conductivity of 10-3M solutions is
measured at room temperature. Table 1shows the
molar conductance values of the complexes which
are located in the range of non-electrolytes22 for all
the complexes.
IR spectra is of great use in structural
elucidation in absence of a powerful technique
like single crystal XRD. The results of the IR
measurements of PAS as well as metal complexes
are tabulated in Table 2 (Fig. 1), wherein the
assignments of the main bands (those affected
by coordination) have been made. The sharp
band at 3495 cm-1 is assigned to the phenoxy
O-H stretching vibration of PAS which disappears
in metal complexes. Whereas, the sharp band at
Magnetic moment and Electronic spectral
studies
The room temperature magnetic moments
of the complexes are in agreement with the spin
Table 1: Physical data with electronic spectra of PAS and its metal complexes
Ligand/
Color
%Yield Melting
µeff.
Molar
n→ p*
p → p*
d → d
Complex
point
(oC)
(B.M.) conductance
(S.m2.mol-1)
(nm)
(nm)
(nm)
SA
Mn(II)
Colorless
Colorless
150
225
> 285
2
2
293
310
301
294
290
315
294
262, 208
262, 214
261
262, 239
262, 238 560, 590
80
5.85
5.05
5.01
2.90
1.75
7.3491
6.90288
9.28186
4.86722
4.92852
8.9688
Fe(II) Reddish brown 75
Co(II)
Ni(II)
Cu(II)
Zn(II)
Magenta
Light green
Dark green
white
78
80
76
85
135
2
> 285
> 285
140
284
276
718
2

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WANI et al., Orient. J. Chem., Vol. 33(3), 1120-1126 (2017)
3387cm-1 is assigned to the N-H stretching vibration to the stretching vibrations of M–OH2 bond18. The
of NH2 group, which is broadened in complexes. medium band at 970cm-1 is assigned to out of
The broadening of this band in complexes may be plane bending g(OH)27, which was disappeared
because of the attachment of water as ligand which in complexes, indicates bonding through phenolic
is also confirmed from thermogravimetric analysis. oxygen atom.Complexes also display week bands in
The broadness may also be because of the presence the region 424–455cm-1.These bands are assigned
of aromatic protons which absorb in the range of to υ(M–O) stretching vibration. The week bands of
3110-3200 cm-125.The characteristic absorption band 970 and 968cm-1 in Ni(II) and Cu(II) complexes may
at 1645cm-1 was observed which can be attributed to be because of the out of plane g(CH) which becomes
asymmetric υ(COO) stretching vibration26, which in near degenerate with g(OH), whose intensity is very
complexes faced red shift (bathochromic shift) with low27. Therefore, from the IR spectra it is concluded
hypochromic effect, suggesting of weakening of C=O that PAS behaves as bidentate ligand with OO
bond and formation of M-O bond.
coordination sites and binds to the metal ions through
carboxylate O and phenolic O atoms.
Complexation is also suggested on behalf
of red shift (bathochromic shift) with hypochromic 1H NMR Analysis
effect in C-O stretching vibrations of complexes to
1H NMR spectra were carried out in DMSO-
that of free ligand PAS (1228cm-1)26. This suggests d6 for the synthesized complex of Zn(II) and ligand
the weakening of C-O bond and formation of stronger PAS. Peak assignments are given in Table 3 for the
M–O bond in complexes. In addition, bands in the corresponding protons and these are numbered
region of 947-904cm-1 and 825cm-1 are assigned in Fig. 2. Disappearance of the peak of phenolic
Fig. 1: IR plots of PAS and its metal complexes
Table 2: IR spectra of PAS and its metal complexes
Complex/ Ligand υ(phe)
υ (NH) υ (COO) (asym) υ(C-O)
g(OH)υ (M-O) (H2O)
υ(M-O)
ASA
3495 s
3387 s
3360 w
1645 s
1607 b
1610 vs
1607 vs
1634 w
1614 w
1605 vs
1228 s
1180 w
1227 w
1180 m
1180 w
1221 w
1205 w
970 m
Mn(II) complex
Fe(II) complex
Co(II) complex
Ni(II) complex
Cu(II) complex
Zn(II) complex
904 w, 825 m
939 vs, 825 s
906 m, 825 s
825 m
905 w, 825m
947 vs, 825 m
455 w
451 vs
451 vs
453 w
455 vs
424 vs
3360 w
3265 w
970 vs
968 w

WANI et al., Orient. J. Chem., Vol. 33(3), 1120-1126 (2017)
proton in the complexes indicate the involvement of
Thermal analysis
1124
the phenolic oxygen atom in complexation (Fig 3).
A shift in the values of ring protons of complexes in
comparison to the proton of PAS also suggests the
complexation. No shift in the peak of NH protons
in complex nullifies the bonding through N atom of
NH2 group. So on the basis of analysis of the results
obtained, it is concluded that the coordination of
the PAS ligand to the metal ions occurs through the
phenolic oxygen and carboxylic oxygen.
The complexes of PAS were also analyzed
thermogravimetrically.The TG curves of complexes
usually refers to three stages of mass losses
within different temperature ranges. The first step
of degradation corresponds to loss of coordinated
water molecules which usually occurs in the range
of 80-150oC.Therefore coordinated water molecules
are confirmed from TGA analysis. Next degradation
steps followed similar degradation trends as is shown
in Figure 4 for Ni(II) complex of PAS.
On the basis of said facts, the proposed
structures for the metal complexes are shown in
Fig. 5. It is suggested that the ligand and metal
combine in 2:1 ratio and metal is coordinated via O
O atoms of the PAS to give octahedral geometry to
the complexes.
Fig. 2: Numbering pattern of carbon containing
protons for 1H NMR peak assignments
Antioxidant activity
Antioxidant activity of PAS and all its metal
complexes were evaluated in terms of DPPH radical
scavenging activity (RSA) at 5 concentrations of
0, 0.5, 1.0, 1.5 and 2 µg/mL of the compound and
corresponding IC50 values were obtained from their
regression plot (Fig.6).Ascorbic acid (AA) was used
as a positive control.PAS and all its metal complexes
show higher activity than the positive control, AA,
with IC50 values 2.75 µg/mL. The highest radical
scavenging activity was observed for Ni(II) complex
with IC50 value 0.88µg/mL and for PAS it was
lower than all the metal complexes with IC50 value
2.13µg/mL.
From the data of IC50 of AA, PAS and its
metal complexes it is evident that all metal complexes
are better antioxidants than PAS and standard AA.
The higher antioxidant activity of metal complexes
than PAS can be explained on some explanations
cited in literature. It is reported by R Milaeva
(2011)28 that the antioxidant activity of sterically
hindered phenolic antioxidants is increased by
metal complexation because: i) Of the modification
in the chemical structures of metal complexes by
changing metal or ligand nature;ii) of the stabilization
Fig. 3: 1H NMR of a) PAS and b) Zn(II) complex
of PAS
Table 3: Peak assignments of protons for 1H NMR of PAS and its Zn(II)
complex
Compound
d (H3), ppm d (H5), ppm d (H6), ppm d (HNH) d (HOH)
PAS
Zn(II) complex
6.09
6.03
6.09
6.03
7.42
7.50
5.96
5.97
11.41

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WANI et al., Orient. J. Chem., Vol. 33(3), 1120-1126 (2017)
Fig. 4:TGA of Ni(II) complex of PAS
Fig. 5: Proposed structure of metal complexes of PAS
Fig. 6: IC50 values of PAS and its metal complexes compared with ascorbic acid
of phenoxyl radical formed with the help of metal ion suggest the surrounding environment of metals in
in the intramolecular redox process and iii) of the these complexes.. The most important conclusion
attachment of functional end-group in order to control drawn from the above investigations is that the
the solubility and transport of complexes. According mono basic bi-dentate ligand is coordinated to the
to Li et al (2010)29, due to the chelation of organic metal ions through Oxygen atoms of carboxylate and
moieties, metal complexes exhibit considerable phenolic atoms. The DPPH assay in terms of IC50
radical scavenging. This view is also supported by values indicates that the PAS and its metal complexes
Tyurin et al (2015)30 that antioxidant effect in metal possess excellent antioxidant properties compared to
complexes is observed due to the presence of an Ascorbic acid, which is a potent reducing agent and
essential organic radical scavenger and redox-active scavenger of free radicals in biological systems and
metal.
can therefore reduce oxidative stress. The study of
these complexes can be an area of interest as these
may affect the bio availability of PAS owing to their
presence in relatively appreciable concentrations in
biological fluids.
The chemical, spectroscopic and thermal
investigation of the complexes of PAS with transition
metal ions viz.Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and
Zn(II) enabled us to determine the composition and

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